1. Field of the Invention
The present invention relates to a display device and a method for manufacturing the display device. Further, the present invention relates to a production system of the display device.
Note that the term “display device” in this specification includes pixel transistors included in a display device and an active matrix substrate provided with a plurality of pixel transistors, as well as the display device itself.
2. Description of the Related Art
In recent years, display devices such as liquid crystal display devices and EL display devices are spreading rapidly. Such display devices are classified roughly into passive matrix display devices and active matrix display devices. In an active matrix display device, an active matrix substrate in which a plurality of switching elements are provided in matrix is used. As a switching element, a transistor is usually used for example.
A general active matrix substrate is provided with a pixel transistor including: a thin film transistor which includes a scan line also serving as a gate electrode, a signal line also serving as a source electrode (or a drain electrode), a semiconductor layer, a drain electrode (or a source electrode); and a protective insulating layer covering the thin film transistor; and a pixel electrode connected to the drain electrode (or the source electrode) in an opening portion provided in the protective insulating layer.
In such an active matrix substrate, a contact resistance of a portion where the drain electrode (or the source electrode) is in contact with the pixel electrode in the opening portion is one of hindrances to improvement of display characteristics (for example, see paragraph [0005] in Patent Document 1).
In addition, in manufacturing an active matrix substrate, it is known that an increase in the number of masks used leads to an increase in the manufacturing cost. Thus, it is well-known that many approaches to reduce the number of masks used have been made, without needing to mention a reference.
Note that, in this specification, the term “mask” includes an etching mask, a photomask, and a protective mask. Note that the “photomask” means a mask layer used in light exposure in a photolithography method, the “etching mask” means a mask layer formed to prevent a film formed under the etching mask from being etched, and the “protective mask” means a mask layer formed to prevent a film formed over the protective mask from being in contact with a layer formed under the protective mask. Note that the “etching mask” and the “protective mask” can each be formed of a resist material, and thus can be referred to as a resist mask in some cases.